Regulating devices for operating control elements in automated transmissions usually have one actuator, one output element and one transmission element by which torque, produced by the actuator, is converted into an actuating force. DC motors are usually used as actuators, in DC motors, a magnetic field produced by a stator generates a flow of current in the electrified conductor of a rotor. The current is usually transmitted to the rotor by the stator, via carbon brushes. That is why such motors are also called brush motors.
DE 102 22 339 A1 discloses this type of arrangement for operating a clutch. A DC motor drives an output element that produces the axial movement of a piston via a ball screw. This makes control of engaging and disengaging a clutch possible. The DC motor is assisted by an energy storage unit when the clutch is disengaged.
DC motors have a speed-torque characteristic with a linear gradient. At high rotational speed that would allow rapid movement, the maximum torque drops. Furthermore, the torque curve of such motors is temperature-dependent. When the temperature increases, the resistance in the windings rises, magnetization by the permanent magnets drops and the current transmitted to the rotor decreases with consequent decline in torque. Particularly when the clutch is actuated, the poorly cooled rotor with the armature windings, where the losses occur, is an additional disadvantage of the brush motor. Due to the losses occurring when used for operating control elements, an energy storage unit is usually necessary in order to relieve the brush motor of the actuating function.
Depending on the construction, DC motors have rotors with a plurality of windings. There is a direct relationship between the number of windings and the maximum torque of a DC motor. In order to achieve a certain torque, DC motors require a minimum rotor diameter that is dependent on the type of construction. The moment of inertia increases as the 4th power of the distance from the center of gravity of the rotor to its axis of rotation, which leads to DC motors having a relatively high moment of inertia. When the mass moment of inertia has to be reduced, the rotor diameter must also be reduced, which leads to a reduction in the efficiency of the motor. Hence, the energy storage unit, described above, also serves the purpose of relieving the electrical system of the vehicle, which is necessary due to the low efficiency of the brush motor.
The brush system of DC motors also has a limited lifetime. Particularly when used in commercial vehicles, sufficient lifetime for brush motors is not always ensured. Also, taking the lifetime of the brush system into account, only a limited brake torque of the actuator can be developed. This leads to longer actuating times.
The task of the present invention is to provide a regulating device for an actuator or control element that is robust, can be adequately cooled and has a high degree of efficiency. In addition, the regulating device should enable a high actuation speed. In order to achieve high speeds, the availability of a high acceleration torque, high rotational speed and high deceleration torque are of decisive importance. In addition, a low mass moment of inertia in the drive motor is a requirement as well.